First evidence found for Red Queen theory
25 February 2010, by Tamera Jones
Evolution happens faster when both parasites and their hosts evolve together, rather than on their own, say scientists. What's more, faster-evolving parasites end up with more diverse genetic sequences, or genomes, than parasites whose hosts don't evolve.
Alice and the red queen.
The findings published this week in Nature are the first to support the so-called Red Queen theory proposed by Lee Van Valen in the early 1970s.
The theory, named after Lewis Carroll's Through the Looking Glass in which the queen tells Alice, 'It takes all the running you can do to keep in the same place,' says that parasites and their hosts are in a constant evolutionary arms race. Each has to evolve ever-better ways of out-witting the other to avoid losing out.
'We've shown that evolution happens at an accelerated pace when two species, in this case host and parasite, evolve together.'
Dr Steve Paterson, University of Liverpool
Although the Red Queen theory is well accepted among scientists as a way of explaining how most species evolve, until now no-one had any concrete evidence to support it.
'Scientists have been confident that the Red Queen does happen, but finding evidence is hard,' says Dr Steve Paterson from the University of Liverpool and lead author of the study.
Evolution happens slowly over many generations. Except, that is, in viruses and bacteria. By using a bacterium called Pseudomonas fluorescens and its fast-evolving viral parasite phage phi2, Paterson and his colleagues were able to analyse hundreds of generations of evolution in action, and so test the validity of the Red Queen theory.
Evolutionary standstill
They prepared two experimental set-ups. In the first, they separated bacteria from their viral parasites to keep the bacteria at an evolutionary standstill, while letting the phage evolve. In the second set-up, the researchers allowed both the bacterium and the phage to evolve adaptations and counter-adaptations. They then used DNA sequencing to look for changes in the virus's genomes.
'It's only because of high through-put DNA sequencing technology that we could sequence so many viruses,' says Paterson. Indeed the Natural Environment Research Council's Biomolecular Analysis Facility in Liverpool, which specialises in DNA sequencing, was a major part of the research team.
After sequencing thousands of virus genomes, they found that the viruses evolved twice as quickly in the second set-up, in which both bacteria and phage were allowed to evolve, as the phages in the first experimental set-up.
These faster-evolving viruses were also more genetically diverse than the first group of viruses, with more mutations.
Paterson and his colleagues predicted that these mutations would be in the genes involved in making the virus infectious. When they looked in detail, the found mutations where they expected them - in a virus structural protein as well as in a so-called tail-fibre protein. Both proteins are crucial for virus infectivity, with the tail-fibre protein being especially important for attaching to the host bacterium.
When the researchers infected the original group of bacteria with the faster-evolving viruses, 'they completely infected all the hosts. There was no resistance at all,' says Paterson.
Although a few genes mutated far from their ancestral state, the majority of phage genes remained the same, suggesting that two species evolving together drives the specific evolution of infectivity genes.
'We've shown that evolution happens at an accelerated pace when two species, in this case host and parasite, evolve together.'
'The next step is to see how fast evolution happens in two species that live in a way that's beneficial to both, so-called mutualist species, which is very different from the host-parasite system,' adds Paterson.
Steve Paterson, Tom Vogwill, Angus Buckling, Rebecca Benmayor, Andrew J. Spiers, Nicholas R. Thomson, Mike Quail, Frances Smith, Danielle Walker, Ben Libberton, Andrew Fenton, Neil Hall & Michael A. Brockhurst, February 2010, Antagonistic coevolution accelerates molecular evolution, Nature, doi:10.1038/nature08798
Received 8 September; accepted 23 December 2009.
Keywords:
Biodiversity,
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